1. Field of the Invention
This invention relates to a pump for feeding fluid at a low flow rate, and more particularly to a fluid feed pump which is suitable for use at a location with a small installation space and can be constructed in a small size.
2. Description of the Related Art
Ink suction pumps (fluid feed pumps) employed in conventional ink jet recording apparatus are formed as pumps of a small size in order to save the installation space. An exemplary one of such space-saving ink suction pumps is disclosed in Japanese Patent Laid-Open Application No. Heisei 3-5160. The ink suction pump disclosed in this document includes a cylinder, a piston disposed in the cylinder and having a piston shaft passing hole formed therein with a seal rib provided at an end face in an axial direction thereof. A piston shaft extends through the piston shaft passing hole and has a piston holder and a piston receiver disposed in a mutually opposing, predetermined spaced relationship from each other on a face of the piston on which the seal rib is provided and another face on the opposite side, respectively.
When the piston shaft is moved in a direction in which the piston holder pushes the piston, ink is sucked into a pump chamber in the cylinder, but when the piston shaft is moved in the opposite direction, the formerly sucked ink is discharged through the piston shaft passing hole.
While the conventional ink suction pump described above is constructed such that a valve function is provided by the end face of the piston on which the seal rib is provided and an end face of the piston holder disposed in an opposing relationship to the end face of the piston, the structure for realizing the valve function and the construction of inlet and outlet paths for ink are complicated. If the sealing performance between an outer circumferential face of the piston holder and an inner face of the cylinder which separate the inside of the cylinder into a suction side section and a discharge side section drops, then when fluid sucked from the suction side section into the pump is to be fed into the discharging side section, fluid in the discharging side section may leak into the suction side section, resulting in failure to obtain a sufficient sucking force. If it is tried to enhance the sealing property, then the problem arises that the frictional resistance between the outer circumferential face of the piston holder and the inner face of the cylinder is increased.
The ink suction pump for the ink jet recording apparatus is required to have a simplified construction and provide a sufficient sucking force.